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Heat and Energy

Heat and Energy. Heat and Temperature. Heat is a type of energy that will flow from a warm area to a colder one. For example …. This cup of coffee will ____ ____ because it is _____ ____ heat energy into the surroundings.

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Heat and Energy

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  1. Heat and Energy

  2. Heat and Temperature Heat is a type of energy that will flow from a warm area to a colder one. For example… This cup of coffee will ____ ____ because it is _____ ____ heat energy into the surroundings. This drink (taken out of the fridge) will _____ ___ because it is _____ ___ heat energy from the surroundings. Words – giving out, warm up, taking in, cool down

  3. Kinetic Theory The particles in a solid vibrate about fixed positions. The bonds are strong, and solids have a fixed shape. Solid The particles in a liquid are close together, but are free to move past one another. Liquids flow. There are still strong bonds between the particles, which must be broken before particles can escape and evaporate. Liquid The particles in a gas are far apart, and can move past each other freely. Gases flow. There are no bonds between the particles. Gas

  4. Conduction Conduction is all about when heat is transferred through a _________. The heat is passed on by ___________ in the molecules. These vibrations get BIGGER when the solid has more ENERGY (i.e. when it is being __________). Metals are _______ conductors than non-metals. This is because the heat is carried by free ________ that can carry the energy around the metal and give it to other electrons and ions. Heating a non-metal Heating a metal Words – vibrations, electrons, solid, heated, better

  5. Convection Convection is all about when a gas or liquid (“fluid”) moves and carries heat with it. When the fluid is heated it ____________. This means that it will become less __________ than the colder fluid around it. Because of this the warmer fluid will try to “_______” over the colder fluid, and this is why warm air rises. This is called a convection ___________. This is how heat reaches us from the ___________ in this room. In CONDUCTION the heat was passed on by VIBRATIONS in a SOLID In CONVECTION the heat is passed on by the FLUID expanding, rising and TAKING THE HEAT with it Words: expands, radiators, dense, heated, current, float

  6. Some questions on convection… • Freezers in supermarkets are often left open to the air. Explain why the food does not melt easily. • Explain why a hot air balloon rises in the air. • Explain why an ice cube floating at the top of a drink will cool all of the drink.

  7. Radiation I’m cool! I’m very hot! Thermal (_________) radiation is the transfer of heat energy by electromagnetic _____. It can pass through a _____ (which is how we get heat from the ____). Anything hot emits thermal radiation. Heat is radiated by the surface – the bigger the surface area, the more radiation. Dark, matt surfaces absorb AND emit a lot ______ heat radiation than white or shiny surfaces. Silvered surfaces ________ almost all heat radiation. Words – Sun, reflect, infrared, waves, more, vacuum

  8. Evaporation Evaporation requires energy. If the most energetic particles evaporate, the average energy of the remaining particles is reduced, and the temperature drops.

  9. The Vacuum Flask Plastic cap filled with foam. Reduces conduction. Silvered on outside to reflect heat radiation away from cold contents. Silvered on inside to reflect heat radiation back to hot contents. Double-walled glass with vacuum between. Stops all conduction and convection.

  10. Specific Heat Capacity The specific heat capacity is the amount of energy needed to raise the temperature of 1 kg of a substance by 1 degree Celcius. Energy transferred = mass x specific heat capacity x temperature change (joules) (kg) J/kgoCoC How much energy is needed to raise the temperature of 2 kg of water by 10oC? (specific heat capacity 4200 J/kgoC) How much energy is needed to achieve the same temperature change in 2 kg of copper? (specific heat capacity 380 4200 J/kgoC)

  11. Energy Heat • There are nine forms of energy: Nuclear Light Kinetic (movement) Sound Elastic potential Chemical Gravitational potential Electrical Energy can never be created nor destroyed – it is only ever converted from one form to another Light (useful) Heat (wasted) Electrical

  12. Energy Transfer Diagrams

  13. House insulation Loft insulation Cavity wall insulation Double glazing Draught excluders U-Value Tells us how much energy passes through per second. The lower the U-value the better the insulator.

  14. House insulation • Which type of insulation costs the most? • Which type of insulation is the most effective? • Which type is the most “cost effective”? • Which type pays for itself after 40 years?

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